Telegrad



Apl 15, 1941.

H. l.. BARNEY ETAL TELEGRAD Filed July a, 1959 4 Sheets-Sheet 1 H. L.BARNEV /NVENTORSI U.$. BERGER AE'. MELHOSE 'ATTORNEY April 15, 11941.fH. L BARNEY Erkl. 2,238,023

TELEGRAD Filed July 8, 1959: 4 Sheets-Sheet 2 ATTORNEY April 15, 1941.H. 1 BARNEY Erm.

TELEGRAD Filed July 8, 1939 4 Sheets-Sheet 'o' HQL. BAR/ver /Nl/N TOR$=as. BERGER A E. MELHOSE ATTORNEY April 15 1941. H. i; BYRNEY TAL2,238,028

TELEGRAD Filed July 8, 1939 4 sheets-sheet 4 ksmo/va sla/VAL oPEnAr/o/vRELEASE or 6.4m o scRfAsE/e i Y .Kops/u TloN 0F RELAys 7oz 7/ LA. o z V)Ivo/ss rHnEsf/QLD AND sENs/r/v/rr snm/c ar wmv mmh-essex I F76. 6 loPERA/ON l l RELEASE or aA//v oscense@ r g LOPE/M rloN 0F RELArs 7a s 7/2 k Il [me-AK sla/VAL No/ss @nsf/ow AND' 1 yg 12v/rr seg/ N535 aygcfgqglTIME 1 @ARA/Er /M/ENTORS: as. BERGER y Af. AfL-Hose secondly,` disablethe enabling circu Patented Apr. 15, 1941 TELEGRAD Harold L. Barney andUriah and Alfred E. Melhose, St.

ors to Bell Telephone rated', New York, N. Y.,

S. Berger, New York, Albans, N. Y., assign- Laboratorle's, Incorpoacorporation of New Application July 8, 1939, Serial N0. 283,368

(Cl. PIB-86) 1.9 claims.

This invention relates to communication systems and particularly totelegraph systems operating over channels subject to iniluences givingrise to great variations in the strength and quality o1' signalsreceived.

The object o1 the invention is to regulate received signals Iin suchmanner as to deliverto receiving apparatus signals of uniform amplitudeand length.

A feature oi' the invention is a telegraph gain regulatingamplifier-detector which will hereinafter be termed a telegrad. 'I'heobject of this device is to regulate telegraph signals received over amutable link such as a badly fading radio circuit and to render suchsignals uniform in strength. A feature oi this circuit is fastiorward-acting gain increasing circuit, a fast baci:-

ward-acting gain decreasing circuit and a gain increase disabler. Thetelegrad has features of similarity to the well-known vogad (voiceoperated gain adjusting device) shown, for instance, in Patent1,853,974, granted April l2, 1932, to Hogg et al., Patent 1,936,658,granted November 2u, 1933, to Bjornson etal., Patent 2,012,810, grantedAugust 27, 1935, to S. Doha, and Patent 2,156,622, granted May 2, 1939,to S. Doba..

The telegrad, however, is designed to be extremely quick acting incomparison to the vogad and, for this reason, novel means have beenincorporated in the new circuit in order that proper control of thedevice may be exercised. For example, both these devices iemploy a gainincreaser disabler for the purpose oi halting the eiect of the gainincreaser when it has increased the gain of a vario-repeater to a givenpoint. Due' to the highalternating currentvoltages at the output of thegain increaser circuit. it is not possible to use a mere relay contactto disable the increaser circuit output. Hence, a feature oi thiscircuit is a two-step device for iirst cutting oi the energizing path tothe gain increasing means and secondly and thereafter to reduce theenabling bias of the gain increasing means.

Expressed in another manner, the gain increaser circuit employed hereinis to a certain extent automatic and comprises two parts, an activatingcircuit and an enabling circuit. The activating circuit starts it intooperation with the enabling bias applied and the disabling means acts tofirst disable the activating circuit and to In both the telegrad andthevogad, the gain o1' the vario-repeater is controlled by the potential ofa condenser. It is, therefore, necessary when this condenser has beencharged to a cerloss and, subsequently,

selves for operating the disabler.

` high loss in the circuit and in another condition inserts a negligibleloss in the circuit while maintaining an approximately even electricalconstant condition therein. This well-known device, shown in Patent1,749,851, granted March 11, 1930, to H. C. Silent, renders the circuitopen for transmission of alternating currents in the low loss conditionand practically opaque for such transmission in the high loss condition.The output of this crossed coil device is connected between a source ofpositive potential and a cold cathode gas tube in the charging circuitof the gain regulating condenser circuit so that energy traversing thecrossed coil device will actuate the cold cathode gas tube and cause aflow of direct current for charging thecondenser. The action is stoppedby first changing the condition oi. the crossed coil device from a lowto a high reducing the positive potential in the condenser chargingcircuit. Thereby. the gain regulating condenser is left at a desiredpotential which may further be regulated by the gain decreaser circuit.

In accordance with another feature of the nvention, economy of apparatusand insurance against dierence in sensitivity between diiferent circuitsis achieved by operating the gain increase disabler from the signalcircuit which is the final output of the telegrad, or, in other words.using the direct current signals them- In the vogads, the gain increasedisabler was part of the vogad and, therefore, required certainapparatus in the nature of an amplifier and detector for operating therelay means which performedthe function of disabling the gain increasercircuit. The telegrad, however, may be considered as the combination ofa vogad and an amplier-detector for operating a signal circuit in whichthe gain increase disabler of the vogad is operated from the signalcircuit beyond the ampliiier-detector. By this means the expense ofproviding the usual ampliiier-detector of the gain increase disabler issaved. Since the disabler is now Worked by the final signal circuit,exact synchronism o1' the ture of this circuit is a pair of relays, thefirst 'of which is directly responsive to the direct current signalsfrom the amplifier-,detector and the second of which is responsive tothe first. Between the rst and second of these relays there is a. delaycircuit so that the second does not move its armature until a specifiedtime after the energization of the first. Through a circuit controlledby the armatures of both these relays. the output signals are controlledat their beginning by the second relay and at their end by the firstrelay. A feature of the invention, then, is a signal timing circuitwhich effectively shortens the output signals by cutting oil a portionof the beginning of each.

Another feature of the invention may be said to reside in the method oftransforming varying strength alternating current signals into equallength direct current signals which consists essentially of three steps;flrst,`the transformation of the different strength alternating currentsignals into uniform strength alternating current signals; second, thetransformation of such uniform strength alternating current signals intodirect current signals, and, third, the adjustment of the length of thedirect current signals to the length of `the original signals. Theintermediate stage signals are spoken of as uniform strengthi signals todenote the fact that regardless of the strength of the original signals,such intermediate stage signals are always approximately the same. Theterm "uniform does not apply to the form of the intermediate signalthroughout its length for such signal is not strictly uniform in thatsense. Actually, due to preliminary filter bulldup and tail-off and dueto the extreme rapidity of the gain increaser action, each signal haswhat may be termed an enlarged head, a major body portion ofapproximately uniform amplitude, and a. gradually decreasing andelongated tail end.

The gain increaser acts so rapidly that by the time the disabler canoperate, and due also tov gives a characteristic enlarged head effect tothe signals.

Where the signals are of the order of twenty milliseconds in length, theenlarged head is of the order of five milliseconds in length and where'the tail end of the signal is elongated in the order of fivemilliseconds, the signal is compensated by cutting off about fivemilliseconds of its head.

It will then be realized that the regulated signals will be displacedsomewhat in time, but, since this displacement is uniform for allsignals, the usual orientation means may be used for purposes ofsynchronization. Another feature of the invention, then, is thecombination of a telegrad comprising a fast-acting vogad, anamplifier-detector beyond the vogad controlling the gain increasedisabler of the vogad and a pulse chopping circuit and an orientationmeans for insuring the correct operation of telegraph receivingmechanism by signals ba'dly distorted in respect of their strength.

The drawings comprise four sheets. The first contains Fig. 1illustrating by a general schematic diagram the manner in which thepresent invention lits into a comprehensive communication system.

Fig. 2 is a circuit diagram showing the telegrad in detail. 'I'hisdiagram is schematic to the extent that in each vacuum tube the heaterelement or filament is merely indicated and the actual connectionsthereto are not shown since the method of making such connections iswell known.

Figs. 3 and 4 are explanatory diagrams illustrating the transition of asignal from fthe signal delivered to the telegrad, the intermediatestage signal and the direct current signal delivered to the signalreceiving apparatus by the telegrad. Fig. 3 shows a strong sign-al andFig. 4 shows a weak signal.

Figs. 5 and 6 are theoretically devised graphs showing the time ofoperation of the various parts of the circuit whereby the intermediatestage signals are properly formed.

Fig. 1 is a general schematic of the system in which the telegrad,subject of the present invention, is employed. A speech path I leads tca hybrid coil 2 from which a path 3 for outgoing speech leads to a vogad4. The outgoing speech then passes through a. transmitting suppressor 5and by means of an amplifier-detector 6 operates a chain of relays 'Ihere labeled as"voice operated switching circuit. This voice operatedswitching circuit controls a transmitting singing suppressor S so thatthe outgoing speech can pass from the transmitting suppressor 5 throughthe delay and amplier 8 and the transmi-tting singing suppressor 9 tothe hybrid coil Ill. From the hybrid coil Ill the speech reaches anotherhybrid coil II and thence goes through the radio transmitter I2 to anantenna I3. Through radio transmission the speech will be received atsome distant point and for purposes of explanation it will be assumedthat the distant point has a receiving circuit similar in all respectsto the lower part of Fig. 1. The speech therefore enters antenna I4,passes through a radio receiver I5 and a repeater i6 4to a hybrid coilI1. From the hybrid coil I'I the speech goes into hybrid coil I8, thencethrough the receiving singing suppressor I9, the receiving repeater 20,a low-pass filter 2I and a path 22 to a hybrid coil such as 2, whence itgoes to the receiving subscriber over a line such as i.

The voice operated switching circuit 1 controls a control tone enabler23 so that a source of control -tone 24 is passed through the controltone filter 25 to `the hybrid coil II and thus accompanies speech. Thevoice operated switching circuit I also controls a switching pointleading from the receiving switching circuit 26 at the same terminal tothe transmitting suppressor 5 so as to open this circuit during theperiods that speech is going out from line I to antenna I3. During thistime the voice operated switching circuit 1 also controls the telegraphcontrol circuit 21 to stop the action of the telegraph transmittingcircuit.

At the receiving end the control tone'with the usual modulation of thecarrier frequency coming in over antenna Il is demodulated in radioreceiver I5 and passes through hybrid coil I'I and thence through atelegraph band elimination lter 28 and into a control tone amplifier andlter 29. This operates the receiving switching circuitl 2l whichperforms several functions as follows. First, the receiving switchingcircuit 25 controls a normally open circuit between the telegraph bandelimination filter 28 and the reeration.

'with side bands about 'l5 celvlnc switching circuit 28 including aspeech ampliiler I0. This is provided so that when control tone is firstreceived the receiving .switching circuit 2t will be operated therebyand then held operated thereafter by speech currents flowing through theamplifier I0.

The receiving switching circuit also controls the receiving singingsuppressor I8 to open up the speech path. The receiving switchingcircuit it also controls a normally closed path between the band-passfilter il and the telegrad 32 so that while speech is being received thetelegrad il `will be disabled` At the same time, the recelving switchingcircuit 2| controls the switching relays for two telegraph channels 33.

During pauses in the speech, either when the subscriber' at the distantend is talking into channel l or during the time when the subscriber onchannel i pauses during his talk out over the antenna i3, the telegraphapparatus u shown in the upper part of the figure is in op- 'llhiscomprises perforator. 3l and 33 Woridny, respectively, into tapetransmitters I8 and il' and thence, into rotary distributor 3i. ltotarydistributor t8 works through the control circuit il which exercisescontrol over the telegraph signal suppressor 39. A source o1' telle-Igraph signal tone is supplied by the telegraph signal oscillator 40 andthrough the action ol the telegraph signal suppressor 3l under controloi' the control circuit 2l sends telegraph signals into the hybrid coilI0, thence through the hybrid coil li and out over the radio transmitterI3.

llt the distant end these telegraph signals. in the iorln of spurts ofalternating current of the usual iorin oi a carrier of the oscillatorfrequency cycles wide caused by the modulation of the carrier by thetelegraph transmitter are received over antenna i4 by the radio receiverl 5 and thence through the repeater to pass through the hybrid coils I'land Il to the band-pass filter 3l. Thereafter, the signals enter thetelegrad k32 and are converted from raryinal strength alternatingcurrent signals to uniiorin strength direct current signals oflprenoticaily the same length at which they were recelved over theantenna I4. These direct current signals then pass through the switchingrelay circuit il and the rotary distributor 4| to the tivo printers liland 43. ol telegraph signals the receiving switching circuit it isunoperated and the speech path is hloclred oil" by the receiving singingsuppressor it. .il line ifi schematically represents a means torlrecping chrouisin with the distant rotary distributor 6l. 'lire rotarydistributor 38 and the rotary clistrihutor lil at the same terminal mayor may not be irept in synchronism.' In actual practice they generallyare lrept in synchronism for reasons haring to do with the cost ofsynchronizing apparatus, 'but from an operating standpoint it is onlynecessary that the rotary distributors form` ing part ofthe same channelbeY kept in synn chronisin.

'The telegrad 32 `is shown in detail in Fig. 2. Signals coming from theband-pass illter 3i pass through a varia-repeater consisting of twostages, first, a copper-oxide vario-losser pad and, secondly, a`push-pull varlable-mu amplifier stage. The signals pass through atransformer 5U and'thence through the copper-oxide variolosser pad totransformer 5I. From transformer 5| they pass in push-pull relationthrough twoy variable-mu suppressor-gridl pentode tubes 82 During thereception the rotary distributor 38 in exact syn and Il tofa transformerI4. The copper-oxide vario-losser pad comprises four copper-oxiderectiers 55, B8, il and Il connected in a bridge circuit across theouter terminals of transformers 50 and 5| across. The outer apex pointsof this bridge are connected in one case to a potentiometer B0 be tweenplus battery and ground, and in the other case ot themid-point of theprimary oi transformer I4. The current iiowing in the coppermilde bridgeis then a function of the plate currents flowing in tubes t2 and 63 sinthe plate current drop across resistance 8l is balanced against thepotential derived from potentiometer it. The larger the plate currentflowing through resistance, the smaller will be the direct currentflowing through the copper-oxide bridge. The important clement in thisvario-repeater is a condenser 6I. The potential oi the upper plate ofvthis condenser determines the gain to the signal. The gain of thevvario-ropeater is increased by raising the positive charge on coudenscr6l and is reduced by a corresponding reverse action adjustment. Throughthe use of a potentiometer 82 the potential oi' the upper plate ofcondenser il may be kept at such a point during idle periods that thevariorepcater is ect at mid-gain g AThe signals going out fromtransformer bil pass through a suppressor-grid pentode tube H3 andthence to a. hybrid coil 84. IThe output oi this hybrid coil works intoa transformer and thence through a suppressor-grid pentode tube 8b,acting as an amplifier, to a transiorlner 6l and thence to a full waverectliier tube til. Under normal conditions, that is, inthe condition oia spacing signal, a suppressor-grid pentode tube 68 is so adjusted bythe potential on the naidpolnt of the secondary of transformer tl thatcurrent flows from the plate oi' tube tu through the neutral relay llland the upper winding' oi relay li, holding them in the positions shown.When a marking signal is transmitted then a direct current voltage isproduced acrossthe diode resistance "l2 and the negative voltage reduces the plate current from tube 69 to the point where relay 'Ilreleases and the biasing current in the lower .winding oi relay 1idrives this relay to its marking contact. When relay 'Il moves from. itsspacing contact, a short circuit on hangover condenser "i3 is removedand this condenser in time is charged by the positive battery connectedthrough the upper winding of relay lt. 'this charging current holdsrelay 'll on its spaclng contact for the hang-over period. Thereafter,as the biasing current through the lower winding of relay 'lll becomeseffective and relay 14 moves to its marking contact, a circuit is closedtrom ground through the armature of relay ll and its marking contact,thence through the armature oi relay to the receiving distributor leadl5.

Since the telegrad is used at the output of a selective dlter 3|, thelength of the pulses reach .ing the input is longer than the signaltransf mitted. Since relay 1I follows the signals at the input of thetelegrad, the circuit including relays ll and 14 and the hang-overcondenser 13 is provided tov regulate `the length of the" pulses goingout on lead l5 to the length oi the pulses before they pass through theband-pass lter 3ll y In general terms, then, alternating currentlmpulses which may vary from strong signals to very weaksignals over arange of some 45 decibels are converted bythe vario-repeater into a1-with a pure resistance 58 bridged there' 'M and its marking contact`-ternating current signals of a practically uniform amplitude, Thesesignals then pass through an amplier-detector` and appear at the outputof the tube 69 as direct current signals and later in the lead as directcurrent signals of uniform strength and of a length equal to the signalsdelivered to the band-pass filter 3|.

It was pointed out above that the potential of the condenser 6I isnormally adjusted by the potentiometer 62 to the point where thevariorepeater is set at mid-gain. If a very weak signal is received, again increaser circuit operates to bring up the gain of thevario-repeater in a very short time. This time, for example, may be aminor fraction of a signal length. For a further specific example, thisperiod may be of the order of 5 to 6 milliseconds, so that where thesignal length is of the order of 22 milliseconds the time taken tochange the gain of the vario-repeater becomes a minor fractionof thesignal length.

The signaling current then passes into a transformer 76 through twoamplifiers comprising essentially two suppressor-grid pentode tubes iland 18 to a variable loss device 19.' When relay 'lll is in the positionshown, the variable loss device 19 is in such condition that thealternating current signal will manifest itself in transformer 80 andthus place an alternating current potential on the terminal of the coldcathode gas-filled tube 8l. This breaks down the gas tube and currentflow therethrough is started, .current flowing from a plus batterythrough the tube Ell, resistance 82 to ground. The drop acrossresistance 82 causes a second cold cathode gas tube 83 to break down andthus apply positive potential to the condenser SI. Since the impedancein this condenser charging circuit is very low, the condenser 6I ischarged rapidly and the gain is changed, for example, in the order of 20decibels in approximately 5 milliseconds.

When the gain has been brought up to the point where a direct currentsignal is produced by the tube 69, manifesting itself through therelease of relay 10 and the movement of relay 'Il from its spacing toits marking contact, this gain increaser circuit is disabled.

The disabling is done in two steps; ilrst, the armature of relay 'l0moves from its front cntact and thus opens the circuit of the variableloss device 19 so that this circuit now becomes opaque to alternatingcurrent and the alternating current ceases to flow in the transformeri0. Thus the circuit for activating the tube Il is disabled. Secondly,and shortly thereafter, when the armature of relay 10 reaches its backcontact, a ground is placed on the lower side of the secondary windingof transformer 80 so that the enabling voltage normally applied to coldcathode tube 8l is reduced.

Heretofore the gain increase disabler of circuits, known as vogads, havebeen operated directly by relay contacts. An analogy would be thecharging circuit for condenser 6| passing through the contacts of relay10. The transient voltage of this circuit, however, on opening thecharging circuit, is so high that the relay con-` tacts cannot be usedalone, and hence the gain increaser is disabled in the two-step mannerjust described, consisting of first disabling the activating circuit,and second in disabling the operating circuit of the gain increaser.

In order to keep the potential on the control condenser 6I from goingtoo high when the gain increaser operates, the condenser 6l is shuntedby a diode rectifier 8l. This limits the voltage of the condenser 6I toa predetermined maximum value.

Two leads coming from the lower part of the hybrid coil 65 lead to atransformer 85 to apply voltage to the control gap of a cold cathodegas-lled tube B6. This breaks down the main gap and causes the controlcondenser 6l to be charged negatively. This circuit constitutes afast-operate backward-acting gain decreaser. This circuit, for example,will reduce the gain by 20 decibels in a period of 4 milliseconds.

Generally the action of the telegrad is as follows. When a weak signalis received, the gain increaser circuit causes the] cold cathode tubesQi and 83 to close the circuit for the charging of condenser Gi from asource of positive potential, which acts to rectify the alternatingcurrent of the signal transmitted through tubes 'l1 and 18.

As the level of the signal at the hybrid coil reaches a predeterminedpoint, the relay Ill will be released and the gain decreaser circuitwill come into operation. Due to certain electrical delays and themechanical delay in the armature travel time of relay 'l0 the gainincreaser is not disabled until the gain has gone slightly above thedesired point. The gain decreaser then adjusts the signal with theresult that a characteristically enlarged head is given to theintermediate stage signal, that is, the signal as it passes through thehybrid coil 64.

When a strong signal is received the gain decreaser and the gainincrease disabler relay 0perate at once subject to the inherentelectrical and mechanical delays in the circuit and the gain increaseris disabled almost immediately again with the result that theintermediate stage signal appears to have a characteristically enlargedhead.

By increasing the speed of the charging circuits of condenser 6i theenlarged head will be made more prominent and by decreasing such speedthe enlarged head may be reduced to a minimum.

When the gain decreaser has brought the potential of condenser 6l downto the proper level, tube 8B will cease to function and the charge oncondenser Si will remain constant thereafter except for the slow driftto mid-gain through potentiometer 62.

This is shown graphically in the two theoretical diagrams of Fig. 5 andFig, 6. Fig. 5 represents a strong signal and Fig. 6 represents a weaksignal. Both of these figures show a graph ofan intermediate stagesignal as plotted between strength of signal and time. In both casesthere is a dotted line a slight distance up on the scale of strength.This represents the noise threshold and the sensitivity of the gainincreaser. As the signal reaches the telegrad, the gain increaser beginsto operate and the gain increase follows the line which ends in a dotand dash line extending in an almost vertical direction in each figure.Some distance up on the strength of signal scale the gainincreasecrosses a dot and dash line marked IOperation of Relays 'I0 and71. This is the operation' of the gain increase disabler. The operatetime of the gain increase disabler, however, allows the gain increase tocontinue until it reaches another dot and dash line further up on thescale of strength of signal. Above this line will be the operation ofthe gain decreaser and below this line will be the release of the gaindecreaser. The gain decreaser, therefore, begins to operate .strength inall cases.

u, letter Y in la well-known code.

' second and,v fourth places.

ci said variable gaindevice.

at a point somewhat above the operation of the gain increase'disablerand theoretically it would operate in a curve similar in shape toa'dotted line passing through this point, but it must be understood thatthis dotted line is only an indication of the type of curve followed andis not an indication of the strength of current in this circuit. The netresult is the deviation of the actual signal from the gain increasegraph. This signal deviated in this manner. reaches a high point andthen begins to come down to the line representing the operate andrelease point of the gain decreaser. At the point A, the gain increasedisabler begins to operate.V At point B,

the gain decreaser begins to affect the signal. Between points B and Cboth the gain increaser and the gain decreaser are operated. At point Cvthe gain increaser has entirely ceased to function due to the completionof the operation of the gain increase disabler and from point C and, topoint D` the` gain decreaser operates to bring the signal down to thedesired level. It

will be noted that the intermediate stage signal is of practically thesame shape and of the same It is conceivable that if rapid fading ofsignals either up or down in f strength is taking' place that furtheradjustments might be made but the characteristic form of the signalsshown in Fig. and Fig. 6

representing a strong signal and Fig. 4 reprei senting a weak signal.These figures have been drawn from oscillograms'derivedfrom actualexperience and` represent the transmission of the In each c'ase you havea marking signal in the first,l third and fth places and a spacingsignal in the The upper line in each case represents the signal as itentersthe band-pass lter 3|. The middleline represents the intermediatestage signal as `it enters the amplifier-detector through theAtransformer 65 and the lower line represents the signal delivered tothe receiving distributor over line 15.

i "of Figs. 3 and 4, are changed first into .uniform strengthalternating current signals, represented 5 nals into equal'lengthuniform strength direct current signals comprising a vario-repeater forchanging varying strength alternating current signals into substantiallyuniform strength alternating current signals, lan ampller-detector forchanging saidy substantially uniform strength alternating currentsignals into direct current signals and means for regulating the lengthof said direct current signals.

4. In a communication system, means for converting varying strengthalternating current signals into equal length uniform strength directcurrent signals comprising a band-pass filter, a vario-repeater forchanging varying strength alternating current signals into substantiallyuniform strength alternating current signals, an amplliier-detector forchanging said substantially uniform strength alternating current signalsinto direct current signals and means for compensating said directcurrent signals for change in length occurring in said conversions.

5. In a communication system, means for convertlng varying strengthalternating current signals into equal length uniform strength directcurrent signals comprising a band-pass filter, .a vario-repeater forchanging varying strength a1- ternating current signals intosubstantially uniform strength alternating current signals,saidvario-repeater being controlled by a `fast-actingk gain increaserresponsive to said varying strength alternating current signals, a gainincrease disabler andl a gain decreaser, an amplifier-detector forchanging said substantially uniform strength structed and arranged toadjust the gain oi said by the middle lines of Figs. 3 and 4, and hallyinto uniform strength direct current signals, as

represented by the bottom lines of Figs.V 3 and 4.

What is claimed is: i l. In a. communication system, a telegradcomprising a variable gain device having a gain increase disabler, anamplifier-detector for operating a signal circuit and means in saidsignal circuit for operating the gain increase disabler 2f. Inacornrnunication system, a signal gain adjusting device, comprising avario-repreater, a forward-acting gain increaser for said variorepeater,a gain increase disabler, and a backward-'acting gainv decreaser forsaid variorepeater, anampliler-detector, a signal circuit responsive tosignals through said vario-repeater and .said amplifier-detector' andmeans in said signal circuit for operating said gain increase disabler.'

3. In a communication system, means for converting varying strengthalternating current sigvario-repeater to a desired signal strengthwithin l a minor fraction of a signal length for changing said varying'strength alternating current signals into substantially uniformstrength alternating current signals, an amplifier-detector for changingsaid substantially uniform strength alternatlng current signals intodirect current signals, means for adjusting the length of saiddirecteur- 'rent signals-to the length ofsaid varying strengthalternating current signals and a gain increase disabler responsive tosaid direct current signals.

7. In a communication system, means for converting varying strengthalternating current sig` nais into equal length uniform strength directcurrent signals comprising a vario-repeater for changing said varyingstrength alternating current signals into substantially uniform strengthalternating current signals and having gain controlling means foradjusting the delivered substantially uniform strength alternatingcurrent signal to ya predetermined value within a minor fraction of thelength of said signal, said gain controlling means comprising afast-acting gain increaser responsive to said varying strengthalternating current signals, a gain increase disabler and a gaindecreaser, an amplifier-detector lor changing said substantially uniformstrength alternating current signals into direct current signals, andmeans to operate sadgain increase disabler by said direct currentsignals at rthe end of said minor fraction of the length ci said signal.

8. In ja communication system, means ior con-n verting ivarying strengthalternating current sig= nais into equal length uniform strength directcurrent signals, comprising a band-pass flirter, a vario-repeater forchanging said varying strength alternating current signals intosubstantially uniform strength alternating current signals, saidvario-repeater being controlled yby a gain in'a creaser responsive tosaid varying strength alternating current signals, a gain increasedisabler and a gain decreaser all constructed `and arranged to function`yithin a minor fraction of a signal length to adjust the deliveredsubstantially uniform strength alternating current signal to apredetermined value, an ampliiier-detector for changing said deliveredsignalsto direct current signals, a first relay responsive to saiddirect current signalsJ a second relay responsive to said first Y relay,a delay circuit for said second relay and a circuit arrangementcontrolled by said relays for delivering uniform strength direct currentsignais, equal in length to rthe length of said varying strengthalternating current signals.

9. In a communication system, means for converting varying strengthalternating current eignals into equal length uniform strength directcurrent signals comprising a vario-repeater for changing said varyingstrength alternating curren-t signals into substantially uniformstrength alternating current signals, said vario-repeater beingcontrolled by a gain increaser responsive to said varying strengthalternating current signals, a gain increase disabler and a gain de- :1

creaser, said gain controlling means being constructed and arranged toadjust the delivered substantially uniform strength alternating currentsignals to a predetermined value Within a minor fraction of a signallength, an amplifierdetector for changing said delivered signals todirect current signals, a rst relay responsive to said direct currentsignals, a second relay responsive -to said first relay, -a delaycircuit for said second relay constructed and arranged rto cause saidsecond relay to operate a minor fraction of a signal-length after .theoperation of said ilrst relay and an output vsignal path controlled bysaid relays in such manner that said second relay controls the beginningof each signal in said output path yand said iirst relay controls theend of each signal in said output path.

10. In Ia communication system, means for changing dii-ferent strengthalternating current signals into direct current signals comprising aband-pass lter and vario-repeater for changing said different strengthalternating current signals into intermediate stage signals, saidintermediate stage signals being elongated by said band-pass filter,means for changing said elongated inter'- mediate stage signals intodirect current signals. and repeating -means for changing said directcurrent signals into uniform strength signals and for adjusting theirlength to be equal to the length of said diierent strength alternatingcurrent signals.

11. In a communication system the method of changing varying strengthalternating current signals into equal length uniform strength directcurrent signals which consist in changing said varying strengthalternating current signals into elongated substantially uniformstrength al.. ternating current signals, changing said elongatedsubstantially uniform strength alternating current signals into directcurrent signals and lll .assenza shortening said direct current signalsto a length equal to said varying strength alternating current signals.

i2. 'in a communication system the method of changing varying strengthalternating current signals into equal length uniform strength directcurrent signals which consists in changing said varying strengthalternating current signals into alternating current signals having anenlarged head, a substantially uniform strength ior a major portion oitheir length and a gradually decreasing and elongated tail, changingsaid last signals into direct current signals and cutting ori' a portionof said direct current signals corresponding to ti enlarged head of saidintermediate c.

i3. In a co', teint-ion system the method of changing varying strengthalternating current signals into equal iength uniform strength directcurrent signals ghi consists in changing said varying strengthalternating current signale into intermediate stage alternating currentsignals each having a body portion of uniform strength, a mini head endportion of steeply rising strength slig o y overshooting the strength ofsaid major body portion and a minor tail end portion of elongated andgradually decreasing strength, changing last signals into direct currentsignals and cutting oil a portion of the head end of each of said directcurrent signals corresponding to the elongation of said inter-A mediatestage signals.

ld. In a communication system means for changing varying strengthalternating current signals into equal length uniform strength directcurrent signals comprising a vario-repeater for changing said varyingstrength alternating current signals into intermediate stage alternatingcurrent signals, a fast-acting gain increaser for said vario-repeater,said gain increaser being responsive to said varying strengthalternating current signals, a gain decreaser for said vario-repeater, again increase disabler responsive to second stage direct current signalswhereby said vario-repeater is controlled by said gain controllers toshape said intermediate stage signals to have a major body portion ofuniform strength, a minor head end portion of steeply rising strengthslightly overshooting the strength of said major body portion and aminor tail end portion of elongated and gradually decreasing strength,an amplier-detector for changing said intermediate stage signals intosecond stage direct current signals, a pulse chopping circuit forchanging said second stage direct current signals into third stagedirect current signals and for delaying the start of said third stageSignals by an amount equal to the elongation of said iirst stagesignals, whereby said third stage signals are delayed in time after saidvarying strength alternating current signals.

15. In a communication system, means for changing varying strengthalternating current signals into equal length uniform strength directcurrent signals, comprising a vario-repeater, a gain increaser for saidvario-repeater comprising a condenser for controlling the bias of saidvario-repeater, a low impedance charging circuit for said condenser andan alternating current path for controlling said charging circuit bysaid varying strength alternating current signals, a gain increasedisabler comprising a crossed coil transmission loss element in saidalternating current path and additional means for stopping the chargingof said condenser, and a gain decreaser for said vario-repeater, anamplier-detector for changing said Aalternating current signals afterpassing through said variorepeater into direct current signals, relaymeans operated by said direct current signals for operating said gainincrease disabler, and relay means operated by said direct currentsignals for delivering direct current signals equal in 'length to saidvarying strength alternating current signals.

16. In a communication system, means for changing varying strengthalternating current signals into equal length uniform strength directcurrent signals comprising a vario-repeater, a

gain increaser for said vario-repeater comprising a condenser forcontrolling the bias of said variorepeater, a low impedance chargingcircuit for said condenser and an alternating current path forcontrolling said charging circuit by said varying strength alternatingcurrent signals, a gain increase disabler comprising a crossed coiltransresponsive to signals at the input oi said variorepeater comprisinga low impedance condenser charging circuit including a cold cathode gastube, and an alternating current path activating' circuit for said coldcathode gas tube, a gain increase disabler comprising a variable losstranse mission device in said alternating current path and quenchingmeans for said cold'cathode gas oas 7 tube, an i means for sequentiallyoperating said variable loss transmission device and said quenchingmeans.

18. In a communication system, a vario-repeater, a gain increaser forsaid vario-repeater responsive to signals at the input oi saidvariorepeater'comprising a low impedance condenser charging circuitincluding a cold cathode gas tube and an alternating current pathactivating circuit for said cold cathode gas tube, a gain increasedisabler comprising a variable loss transmission device in saidalternating current path and quenching means for said cold cathode gastube, a direct current relay responsive to the output of saidvario-repeater and contact means operated by said relay for iirstoperating said variable loss transmission device and second operatingsaid quenching means.

19. In a communication system, means for changing varying strengthalternating current signals of the order` of twenty milliseconds inlength into equal length uniform strength direct current signalscomprising a vario-repeater, having a gain increaser responsive to saidvarying strength alternating current signals, a gain decreaser and again increase dlsabler constructed and arranged to change said varyingstrength alternating current signals into uniform strength alternatingcurrent signals within a period of the order of five milliseconds, anamplifier-detector for changing said uniform strength alternatingcurrent signals into direct current signals, relay means responsive tosaid direct current signals for operating said gain increase disablerand relay means also responsive to said direct lcurrent signals forrepeating said direct current signals and for rendering said repeatedsignals shorter in length by a period of the order of ilve milliseconds.

HAROLD L. BARNEY. URIAH S. BERGER. 'ALFRED E. MELI-IOSE.

